Many thanks for your replies, Bob and Prof Inggs. Now we have a better idea how to tackle the issue.
Cheers. On Fri, Oct 19, 2018 at 12:37 PM Michael Inggs <[email protected]> wrote: > Hi Nitish > > I am sure the Meinberg TTL will battle to drive 20 mA into the SNAP. It > is probably rated at a few TTL loads. > > For multiple boards, you will need to buffer the output of the Meinberg > into a clock distribution network i.e. multiple output gate / driver > leading to the number of boards you aim to drive as separate TTL channels. > This is a bit pedantic, but just linking the Meinberg in parallel to a > number of TTL inputs (check the Meinberg drive capability in TTL loads in > the first place) will lead to multiple reflections and some jitter on the > leading edge. > > For our NeXtRAD multistatic radar that uses GPS synchronisation between > nodes, we have implemented an ubiquitous Frequency Distribution Unit (FDU) > that can swallow almost any 10 MHz or 100 MHz clock, at all the weird logic > levels around, and then providing 10 and 100 MHz in 6 ports per voltage > standard (5V, 3V3, sinewave). There is an optional 10x multiplier (low > phase noise) for converting from 10 MHz to 100 MHz. Block diagram attached. > You can implement any subset of it. Can provide board layouts etc. > > We also have a home made GPS Disciplined Oscillator that is proved to > provide less that 4 ns rms jitter between nodes with common view > satellites. It provides 1 pps, 10 and 100 MHz outputs (at various levels). > Stephan Sandenbergh is the father of this, and has implemented some cunning > fast lock mechanisms. Otherwise you will be there for hours if the power > goes off. > > Stephan also built a test jig for comparing two sources and plotting the > Allen Variance. Be careful of low cost GPSDOs as they are designed for NTP > applications in networks, where 15 ms is all that is required. > > We also have a great deal of experience and hardware (with results) of > using White Rabbit to synchronise receivers. > > Regards > > On Fri, 19 Oct 2018 at 09:04, Nitish Ragoomundun < > [email protected]> wrote: > >> >> Hi all, >> >> We are building a low-frequency array for the observation of the >> deuterium hyperfine line at 327.4 MHz with a bandwidth of 250 kHz. We >> intend to use SNAPs for acquisition. The boards will operate at full 12 >> channels input, thus the ADCs at 250 MSps. We will subsequently decimate >> the data rate, as our working bandwidth is narrow. >> >> Concerning the clock input for the SNAP, >> https://casper.berkeley.edu/wiki/SNAP states the following: >> >> *Digital 1 PPS: 50 ohm single-ended LVTTL logic levels * >> >> - * SMATP13 * >> - * Vin-high 2.0 to 3.3 Volts. Low current drive sources, such as >> typical LVTTL or CMOS gates, probably can not supply the 40mA required to >> supply the 2.0V into the 50ohm load. * >> - * Vin-low 0.0 to 0.8 Volts* >> >> >> Actually we considered buying the GPS-disciplined Meinberg M500 LANTIME ( >> https://www.meinbergglobal.com/english/products/modular-railmount-ntp-server-ieee-1588-solution.htm), >> which is advertised to output 1 PPS *TTL* levels. Now, our first >> question is whether the SNAP can work with this? Also, the note about low >> current drive sources is a little confusing, can anyone shed some light >> here. >> >> Secondly, we would like suggestions from anyone who has experience with >> clocking the SNAP. You see, we run a very tight budget and the M500 LANTIME >> clock is expensive. We would like to know if there is a less costly way to >> clock the SNAP and synchronise several boards. >> >> Thanks. >> >> Best regards, >> Nitish Ragoomundun >> Department of Physics >> University of Mauritius >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To post to this group, send email to [email protected]. >> > > > -- > Michael Inggs > 10 Devon Street, Simon's Town, South Africa. Tel: +27 21 786 1723 Fax: +27 > 21 786 1151 Skype: mikings Cell: +27 83 776 7304 > "Ex Africa semper aliquid novi" > > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > -- You received this message because you are subscribed to the Google Groups "[email protected]" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected].
